I. Field of the Invention
The present invention relates generally to compositions providing superior thermal insulation. More particularly, the invention relates to composition comprising liquids with low thermal conductivity, such as a halocarbon oil, emulsifying agents, and microcapsules. The invention also relates to the use of these compositions in various insulating garments.
II. Description of the Related Art
Thermal protection for divers and underwater cabins (e.g., chambers, submersible hulls, waterproof housings, etc.) is an area that has garnered considerable research effort. Much of this research has focused on passive methods for thermal insulation. Passive methods for thermally protecting a submerged cabin or diver from extreme cold water exposures share a common advantage over their active heating alternatives, namely there is no requirement for energy storage or energy distribution. This advantage tends to make passive thermal protection systems less complex, and usually less expensive. Unfortunately, in extremely cold waters, passive systems have customarily required the use of thick, layered insulating materials. For instance, such passive systems often require that divers wear either foam neoprene or fibrous batts beneath waterproof jackets to reduce the loss of heat to the surrounding cold water.
These conventional insulating materials suffer from several disadvantages. For instance, the materials tend to be excessively bulky, thereby inhibiting mobility when used by divers. Such materials are also normally inherently buoyant. This is undesirable because it necessitates the use of lead weights or other ballasting materials to make the insulating medium neutrally buoyant. Furthermore, conventional materials typically used in passive insulating systems usually are highly variable in insulating effect due to compression of the materials that is caused by the increased hydrostatic pressure as depth increases. Finally, it is often difficult to keep conventional materials waterproof The failure of the materials to maintain an impermeability to water could fatally reduce the degree of thermal protection afforded by the materials.
Syntactic foams, rigid polymers loaded with hollow glass microballoons, have frequently been utilized as an insulating medium for deep underwater applications where mobility is not a concern due to their minimal compressibility. However, similar to foam neoprene and insulating batt materials, syntactic foams are buoyant and have only moderate insulating capability.
The shortcomings of the insulating materials of the prior art may be readily seen by examining, for example, traditional diver gloves. A diver's ability to perform meaningful work is greatly diminished in long-duration missions if his hands are cold when the mission objective has been reached. Unfortunately, in extremely cold water diving, conventional gloves use thick, foam neoprene or layered insulating materials worn beneath waterproof glove shells to reduce the loss of body heat to the surrounding cold water. These gloves tend to be a) excessively bulky —inhibiting finger sensitivity and manual dexterity; b) inherently buoyant; c) highly variable in insulating effect due to material squeeze as hydrostatic pressures increase; and d) difficult to keep waterproof—an uncertainty that could fatally reduce the diver's thermal protection during long-duration missions. This dilemma between thermal protection and manual dexterity has often forced the diver to make decisions about how to maximize his performance using inadequate equipment. Accordingly, a need still therefore exists for an insulating material that possesses minimal bulk, low thermal conductivity, and neutral buoyancy.